The title is a bit over dramatic but, per the title, if you could contribute with one piece of knowledge to a book that every single individual should learn from in order to kickstart a civilization, what would be yours?
My personal choice would be the process of soap making, from scratch.
Considering no one has truly figured out how to make a Democracy survive, I’m impressed this is your contribution. You should probably be writing books before this one, if you have answers.